#ColoradoRiver: Aspinall Unit operations update #COriver

Blue Mesa Reservoir
Blue Mesa Reservoir

From email from Reclamation (Erik Knight):

The April 1st forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 515,000 acre-feet. This is 76% of the 30 year average. Snowpack in the Upper Gunnison Basin is currently 87% of average. Blue Mesa Reservoir current content is 558,000 acre-feet which is 67% of full. Current elevation is 7487.0 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.

Black Canyon Water Right

The peak flow and shoulder flow components of the Black Canyon Water Right will be determined by the May 1 forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir. If the May 1 forecast is equal to the current forecast of 515,000 acre-feet of runoff volume, the peak flow target will be equal to 3,197 cfs for a duration of 24 hours. The shoulder flow target will be 300 cfs, for the period between May 1 and July 25. The point of measurement of flows to satisfy the Black Canyon Water Right is the Gunnison River below Gunnison Tunnel streamgage at the upstream boundary of Black Canyon of the Gunnison National Park.

Aspinall Unit Operations ROD

Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the peak flow and duration flow targets in the lower Gunnison River, as measured at the Whitewater gage, will be determined by the forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir and the hydrologic year type. At the time of the spring operation, if the forecast is equal to the current forecast of 515,000 acre-feet of runoff volume, the hydrologic year type will be set as Moderately Dry. Under a Moderately Dry year the peak flow target will be 8,029 cfs and the duration target at this flow will be 1 day.

Projected Spring Operations

During spring operations, releases from the Aspinall Unit will be made in an attempt to match the peak flow of the North Fork of the Gunnison River to maximize the potential of meeting the desired peak at the Whitewater gage, while simultaneously meeting the Black Canyon Water Right peak flow amount. The magnitude of release necessary to meet the desired peak at the Whitewater gage will be dependent on the flow contribution from the North Fork of the Gunnison River and other tributaries downstream from the Aspinall Unit. Current projections for spring peak operations show that flows in the Gunnison River through the Black Canyon could be between 5,000 cfs and 5,500 cfs for 1 day in order to achieve the desired peak flow and duration at Whitewater. If actual flows on the North Fork of the Gunnison River are less than currently projected, flows through the Black Canyon could be even higher. With this runoff forecast and corresponding downstream targets, Blue Mesa Reservoir is currently projected to fill to an elevation of around 7508.5 feet with an approximate peak content of 733,000 acre-feet.

Fog-filled Black Canyon via the National Park Service
Fog-filled Black Canyon via the National Park Service

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